Guest geology by David Middleton
Cenozoic Era: The Era of New Life
Who would have ever guessed that details about the first day of the Cenozoic Era might have been preserved the stratigraphic record?
Sep 09, 2019
Rocks at Asteroid Impact Site Record First Day of Dinosaur Extinction
AUSTIN, Texas — When the asteroid that wiped out the dinosaurs slammed into the planet, the impact set wildfires, triggered tsunamis and blasted so much sulfur into the atmosphere that it blocked the sun, which caused the global cooling that ultimately doomed the dinos.
That’s the scenario scientists have hypothesized. Now, a new study led by The University of Texas at Austin has confirmed it by finding hard evidence in the hundreds of feet of rocks that filled the impact crater within the first 24 hours after impact.
The evidence includes bits of charcoal, jumbles of rock brought in by the tsunami’s backflow and conspicuously absent sulfur. They are all part of a rock record that offers the most detailed look yet into the aftermath of the catastrophe that ended the Age of Dinosaurs, said Sean Gulick, a research professor at the University of Texas Institute for Geophysics (UTIG) at the Jackson School of Geosciences.
“It’s an expanded record of events that we were able to recover from within ground zero,” said Gulick, who led the study and co-led the 2016 International Ocean Discovery Program scientific drilling mission that retrieved the rocks from the impact site offshore of the Yucatan Peninsula. “It tells us about impact processes from an eyewitness location.”
The research was published in the Proceedings of the National Academy of Sciences on Sept. 9 and builds on earlier work co-led and led by the Jackson School that described how the crater formed and how life quickly recovered at the impact site. An international team of more than two dozen scientists contributed to this study.
This bit is really interesting:
The evidence includes bits of charcoal, jumbles of rock brought in by the tsunami’s backflow and conspicuously absent sulfur.
While paleoclimatological evidence for a post-Chicxulub global cooling/darkening is limited (Vellekoop et al., 2014), the absence of sulfur-rich rocks in the crater backfill is a pretty good indication that the sulfur-rich evaporite rocks in the impact area were vaporized.
The first day of the Cenozoic
Highly expanded Cretaceous–Paleogene (K-Pg) boundary section from the Chicxulub peak ring, recovered by International Ocean Discovery Program (IODP)–International Continental Scientific Drilling Program (ICDP) Expedition 364, provides an unprecedented window into the immediate aftermath of the impact. Site M0077 includes ∼130 m of impact melt rock and suevite deposited the first day of the Cenozoic covered by <1 m of micrite-rich carbonate deposited over subsequent weeks to years. We present an interpreted series of events based on analyses of these drill cores. Within minutes of the impact, centrally uplifted basement rock collapsed outward to form a peak ring capped in melt rock. Within tens of minutes, the peak ring was covered in ∼40 m of brecciated impact melt rock and coarse-grained suevite, including clasts possibly generated by melt–water interactions during ocean resurge. Within an hour, resurge crested the peak ring, depositing a 10-m-thick layer of suevite with increased particle roundness and sorting. Within hours, the full resurge deposit formed through settling and seiches, resulting in an 80-m-thick fining-upward, sorted suevite in the flooded crater. Within a day, the reflected rim-wave tsunami reached the crater, depositing a cross-bedded sand-to-fine gravel layer enriched in polycyclic aromatic hydrocarbons overlain by charcoal fragments. Generation of a deep crater open to the ocean allowed rapid flooding and sediment accumulation rates among the highest known in the geologic record. The high-resolution section provides insight into the impact environmental effects, including charcoal as evidence for impact-induced wildfires and a paucity of sulfur-rich evaporites from the target supporting rapid global cooling and darkness as extinction mechanisms.
The very high sediment accumulation rate in the crater enables very detailed resolution of the events 65 million years ago. While the exact day of the impact can’t be identified, the events of that day and the following weeks can be reconstructed in great detail.
The paper is pay-walled; but it might just be worth $10. The SI includes this seismic profile, showing how their core ties into the crater.
Just 60 km away from the impact site, the Yaxcopoil-1 CSDP core encountered a thick evaporite sequence just below the layer of impact breccia:
Lithologies of units A, C, D and F are dominated by dolomites and anhydrites and indicate restricted interior carbonate platform environments (Fig. 2). Dolomites were likely deposited in very shallow
subtidal to intertidal environments, as also indicated by the presence of mudstone lithologies, anhydrite nodules, laminated dolomite of likely stromatolitic origin, and the generally low abundance of megafossils (only rare bivalve fragments). Miliolids are often the only benthic
foraminifera recovered from these intervals and they are very rare. Alternating sequences of anhydrite and dolomite and massive anhydrite units are interpreted to indicate deposition in sabkha environments.
Anhydrite (CaSO4) is one of the most common evaporite minerals.
It’s been estimated that the Chicxulub impact may have injected far more sulfate aerosols into the upper atmosphere than any other known Phanerozoic Eon impact event.
[T]he total sulfur degassing from the evaporite-rich sediments in the Chicxulub impact site may have led to formation of 3.8 × 1018 to 1.3 × 1019 g sulfate aerosol, and global atmospheric mass loading from the sulfate aerosol alone is estimated to be of the order of 1–2.6 g cm−2.
To provide a frame of reference, Mount Pinatubo only injected about 20 million metric tons of sulfur dioxide into the stratosphere:
Several eruptions during the past century have caused a decline in the average temperature at the Earth’s surface of up to half a degree (Fahrenheit scale) for periods of one to three years. The climactic eruption of Mount Pinatubo on June 15, 1991, was one of the largest eruptions of the twentieth century and injected a 20-million ton (metric scale) sulfur dioxide cloud into the stratosphere at an altitude of more than 20 miles. The Pinatubo cloud was the largest sulfur dioxide cloud ever observed in the stratosphere since the beginning of such observations by satellites in 1978. It caused what is believed to be the largest aerosol disturbance of the stratosphere in the twentieth century, though probably smaller than the disturbances from eruptions of Krakatau in 1883 and Tambora in 1815. Consequently, it was a standout in its climate impact and cooled the Earth’s surface for three years following the eruption, by as much as 1.3 degrees F at the height of the impact.
In terms of sulfate aerosols, the Chicxulub impact could have been the equivalent of 190,000 to 1,900,000 Mount Pinatubos.
Had the impact occurred in an area devoid of sulfur-rich evaporites, the K-Pg extinction would have been far less severe.
Mount Pinatubo injected about 20 million metric tons of sulfate aerosols into the stratosphere and caused about 0.7 °C of cooling, offsetting over 100 years of Gorebal warming for about three years. Pinatubo also injected about 50 million metric tons of CO2 into the atmosphere and caused no warming.
The Chicxulub impact put 190,000 to 1,900,000 Mount Pinatubos worth of sulfate aerosols into the upper atmosphere within a few days and left a big @$$ mark in the stratigraphic record. Humans have accounted for less than 1% of the cumulative CO2 emissions since 1751, yet we’re supposedly causing a “climate crisis” that rivals the PETM, Chicxulub impact and end-Permian extinction combined (Sarc?).
Did you ever wonder why past examples of volcanic greenhouse gas driven climate crises don’t seem to survive scrutiny?
While it has been proposed that intense volcanic release of carbon dioxide in the deep geologic past did cause global warming, and possibly some mass extinctions, this is a topic of scientific debate at present.
There is virtually no evidence that past volcanic releases of CO2 actually caused any discernible warming. Seawater pCO2 was higher before and after the oft-cited Paleocene-Eocene Thermal Maximum (PETM), which was sort of contemporaneous with the emplacement of the North Atlantic Large Igneous Province..
Note how the PETM (55 Ma) is about as far from a CO2 analog to modern times as it possibly could be… unless the PETM stomata data are correct, in which case AGW is even more insignificant than previously thought.
Regarding temperatures, the PETM is also about as far from being an analog to modern times as it possibly could be.
The Cretaceous and Paleogene Periods were warm. Whatever impact-related cooling that did occur, was of too short a duration to be resolved. But at least there’s some evidence for it. It has been postulated that the the initial effect of the Chicxulub impact was a sharp rise in temperature associated with the fireball and subsequent firestorms, followed by aerosol-induced cooling and then greenhouse warming (?)…
While there is evidence of the first two phases, the subsequent greenhouse warming is entirely speculative, based on recent assumptions about climate sensitivity to CO2. Assumptions that were largely scoffed at as recently as the late 1970’s.
Suggestion that changing carbon dioxide content of the atmosphere could be a major factor in climate change dates from 1861, when it was proposed by British physicist John Tyndall.
Unfortunately we cannot estimate accurately changes of past CO2 content of either atmosphere or oceans, nor is there any firm quantitative basis for estimating the the magnitude of drop in carbon dioxide content necessary to trigger glaciation. Moreover the entire concept of an atmospheric greenhouse effect is controversial, for the rate of ocean-atmosphere equalization is uncertain.
Dott & Batten, 1976
The same assumption, that the high CO2 levels can be directly related to increased volcanic activity during the mid-late Cretaceous Period, is not well-supported by any observations, present or past.
The highest Cretaceous CO2 levels preceded the 125-115 Ma peak in volcanic activity by 15 million years.
Nor is there a particularly good correlation between atmospheric CO2 and temperature…
If there was a clear relationship between volcanic activity, CO2 and temperature, we should see it in the rocks, particularly the basalt formations of the Columbia River Basalt Group (CRBG), the most recent, and best preserved flood basalt sequence.
According to Kashbohm & Schoene (2018)…
Flood basalts, the largest volcanic events in Earth history, are thought to drive global environmental change because they can emit large volumes of CO2 and SO2 over short geologic time scales. Eruption of the Columbia River Basalt Group (CRBG) has been linked to elevated atmospheric CO2 and global warming during the mid-Miocene climate optimum (MMCO) ~16 million years (Ma) ago. However, a causative relationship between volcanism and warming remains speculative, as the timing and tempo of CRBG eruptions is not well known. We use U-Pb geochronology on zircon-bearing volcanic ash beds intercalated within the basalt stratigraphy to build a high-resolution CRBG eruption record. Our data set shows that more than 95% of the CRBG erupted between 16.7 and 15.9 Ma, twice as fast as previous estimates. By suggesting a recalibration of the geomagnetic polarity time scale, these data indicate that the onset of flood volcanism is nearly contemporaneous with that of the MMCO.
It does appear that the timing of the vast majority CRBG eruptions can be fairly well tied down to a 700,000 to 900,000 year period coincident with the Mid-Miocene Climatic Optimum. However, even with the prodigious volume of CO2 associated with flood basalt eruptions, it’s not enough to significantly move the “climate needle”:
A statistic: It is estimated that an erupting basalt lava flow with a volume of 2000 km3 would release approximately 7 billion tonnes of carbon (or 26 billion tonnes of CO2).
This is about the same as the amount currently released by burning of fossil fuels – each year.
Armstrong McKay et al., 2014 estimated that the main phase of the CRBG eruptions, along with “cryptic degassing” of country rock, etc., emitted 4,090 to 5,670 billion tons of carbon over a 900,000 period. This only works out to 5-6 million tonnes of carbon per year… That’s an order of magnitude less than a rounding error. Our current 10 billion tonnes per year is only equivalent to 3% of the total annual sources in the Earth’s carbon budget. Self et al., 2005 found that CO2 emissions from flood basalt eruptions were insignificant relative to the mass of CO2 in the atmosphere and unlikely to have played a signifcant role in past episodes of “global warming.” Although they did note that the sulfur gas emissions may truly have been unprecedented.
While the impact of volcanic S gas release may be profound, the mass of CO2 directly released by individual flood lava eruptive events is tiny in comparison to the normal mass in the troposphere and stratosphere. The predicted increases in atmospheric concentration are a fraction of the current anthropogenic CO2 released from hydrocarbon burning (~25 Gt per year). Moreover, while the amount of CO2 in the atmosphere is currently ~3000 Gt, it was perhaps double this value during the late Cretaceous (i.e. ~6000 Gt). It is therefore unlikely that volcanic CO2 had a direct effect on mechanisms of global warming, supporting earlier findings by Caldeira and Rampino (1990). In addition, there would have been more than sufficient time for the extra mass of CO2 added to equilibrate, given that the lava-forming eruptive events must have been spaced at least hundreds, and probably thousands, of years apart. By contrast, SO2 emissions and the atmospheric burden of sulfate aerosols generated during flood basalt events appear to be unprecedented at any other time in Earth history. Acid rain may also have been widespread. What is less certain is whether affected biota would have had time to recover from the deleterious effects of sulfate aerosol clouds and acid rain, although quiescent intervals lasting millennia appear to offer ample time for the recovery of local biological and environmental systems (Jolley 1997).
Self et al., 2005
We can’t even be certain that the atmospheric concentration of CO2 during the Mid-Miocene Climatic Optimum was significantly elevated relative to the extremely low values of the Quaternary Period.
We can see that CO2 estimates for MMCO range from 250 to 500 ppm, rendering any efforts to draw conclusions about the CRBG and MMCO totally pointless. According to Pagani et al, 1999:
There is no evidence for either high pCO2 during the late early Miocene climatic optimum or a sharp pCO2 decreases associated with
Pagani et al., 1999
Pagani et al., suggest that changes in oceanic circulation driven by plate tectonics (opening of the Drake Passage) and the presence (or lack thereof) of a large polar ice sheet were the primary drivers of Miocene climate change, not volcanic activity. Same as it ever was…
FORECASTING THE FUTURE. We can now try to decide if we are now in an interglacial stage, with other glacials to follow, or if the world has finally emerged from the Cenozoic Ice Age. According to the Milankovitch theory, fluctuations of radiation of the type shown in Fig. 16-18 must continue and therefore future glacial stages will continue. According to the theory just described, as long as the North and South Poles retain their present thermally isolated locations, the polar latitudes will be frigid; and as the Arctic Ocean keeps oscillating between ice-free and ice-covered states, glacial-interglacial climates will continue.
Finally, regardless of which theory one subscribes to, as long as we see no fundamental change in the late Cenozoic climate trend, and the presence of ice on Greenland and Antarctica indicates that no change has occurred, we can expect that the fluctuations of the past million years will continue.
Donn, William L. Meteorology. 4th Edition. McGraw-Hill 1975. pp 463-464
Despite only having 12 years to solve the “climate crisis,” we are still living in an Ice Age, and will be so long as Antarctica remains isolated over the southern polar region, Greenland retains its ice sheet and the northern polar region retains at least seasonal ice cover.
The roughly 1.0 °C of warming since the coldest climatic period of the Holocene, the Little Ice Age, hasn’t budged us out of the Quaternary Period temperature “noise level.”
Another 0.5 to 1.0 ºC between now and the end of the century doesn’t even put us into Eemian climate territory, much less the Miocene or even the Pliocene. We will still be in the Quaternary Period noise level. Bear in mind that the instrumental temperature data are of much higher resolution than the δ18O derived temperatures. As such, the δ18O data reflect the bare minimum of dynamic amplitude range. Actual paleo temperatures would have reflected a far greater range of variability (higher highs and lower lows).
On the other hand, a Chicxulub-style impact could easily slap our rather cold climate back into Pleistocene glacial conditions faster than the Green New Deal could destroy our robust economy.
Armstrong McKay, David, Toby Tyrrell, Paul A. Wilson, & Gavin Foster. (2014). “Estimating the impact of the cryptic degassing of Large Igneous Provinces: A mid-Miocene case-study”. Earth and Planetary Science Letters. 403. 254–262. 10.1016/j.epsl.2014.06.040. Special thanks to David Armstrong McKay for kindly sending me a copy of his paper.
Berner, R.A. and Z. Kothavala, 2001. GEOCARB III: A Revised Model of Atmospheric CO2 over Phanerozoic Time, American Journal of Science, v.301, pp.182-204, February 2001.
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via Watts Up With That?
September 10, 2019 at 08:18PM